Indirect thermal electron gun and method of using the same

Abstract

The present invention discloses an indirect thermal electron gun and its use method. The positive ions in the plasma generated by gas discharge in the electron gun bombard an aluminum cathode, generating secondary electrons at the aluminum cathode. The secondary electrons are accelerated by the electrostatic field formed by the aluminum cathode and a tungsten needle and bombard the tungsten needle, converting kinetic energy into thermal energy, heating the tungsten needle, causing the tungsten needle to reach a thermal emission state and emit electrons. The size of the electron beam emitted by the tungsten needle is regulated by a negative gate voltage. Then, through the electrostatic convergence system formed by the gate and anode and the electromagnetic convergence system on the beam channel, the electron beam emitted by the tungsten needle obtains a small beam spot with highly concentrated electron beam energy on the surface of the workpiece. The present invention combines the advantages of existing hot cathode electron gun and cold cathode electron gun technologies, not only having a long cathode life, but also being able to obtain a small electron beam spot with highly concentrated electron beam energy density, meeting the requirements of electron beam precision machining and manufacturing processes.

Description

Technical Field

[0001] The present invention belongs to the technical field of electron guns, and in particular relates to an indirect thermal electron gun and a method for using the same. Background Art

[0002] In recent years, electron beam additive manufacturing (EBAM) technology has developed rapidly, and components manufactured using EBAM have found widespread application in aerospace, military equipment, and medical applications. EBAM, which includes EB fuse deposition and EB selective melting, requires a stable, long-term electron beam source to manufacture large metal components.

[0003] However, the electron beam sources currently used in electron beam additive manufacturing equipment are generally hot cathode electron beam sources. Commonly used electron guns for hot cathode electron beam sources mainly include directly heated electron guns and indirectly heated electron guns. Directly heated electron guns emit electrons by heating a filament, which serves as the cathode. Indirectly heated electron guns heat the filament and then adjust the bombardment voltage between the filament and the cathode, causing the electrons emitted by the filament to accelerate under the action of the bombardment voltage and bombard the cathode, converting kinetic energy into thermal energy, heating the cathode, and then causing the cathode to emit electrons. To ensure the long-term stable operation of hot cathode electron beam sources, the cathode life must be sufficiently long, which places stringent requirements on the selection of cathode materials and structural design. Existing cathodes are generally made of tungsten ribbon to form a "V" structure, or tungsten wire to form a mosquito coil structure. Furthermore, both directly heated and indirectly heated electron guns require a filament, which emits electrons and is susceptible to positive ion corrosion. This makes the filament or cathode susceptible to metal vapor contamination, especially under high-power electron beam output conditions. Furthermore, after a period of use, the cathode inevitably deforms, making it difficult to significantly increase the lifespan of the filament or cathode, affecting the beam quality and cathode service life of the electron beam source. A short cathode lifespan also leads to frequent cathode replacement during the forming process of large metal structures, which not only affects production efficiency but also adversely affects the forming quality. Therefore, existing hot cathode electron beam sources are unable to meet the demand for long-life electron beam sources for electron beam additive manufacturing of large metal structures.

[0004] In recent years, research on the use of coaxial cold cathode electron beam additive manufacturing (CEBM) has significantly improved cathode lifespan. However, due to the limited working distance of the CEBM, typically only 30mm to 40mm, its spatial accessibility is poor, making it difficult to adapt to the rapid prototyping of large and complex components. Application No. 2014107758547 discloses a high-voltage gas discharge electron gun device. While this device increases the operating voltage of the gas discharge electron gun and extends cathode lifespan, the beam spot of conventional gas discharge cold cathode electron guns is generally large, typically reaching diameters of several to tens of millimeters, making it unsuitable for precision electron beam machining and manufacturing technologies such as electron beam selective melting (EBM) and electron beam welding. Therefore, existing cold cathode electron beam sources struggle to meet the high-precision requirements of EBBM for large metal structures. Summary of the Invention

[0005] Purpose of the invention: In response to the problems existing in the prior art, the present invention discloses an indirect thermal electron gun and a method for using the same, which not only greatly improves the service life of the cathode, but also can obtain a small beam spot with highly concentrated electron beam energy density, which can meet the demand for long-life, high-precision electron beam sources in electron beam additive manufacturing of large metal structures.

[0006] Technical solution: To achieve the above-mentioned purpose, the present invention adopts the following technical solution:

[0007] A thermal electron gun includes a first gun body and a second gun body, wherein the first gun body and the second gun body are both cylindrical structures and the facing end faces are connected, a partition is provided at one end of the second gun body close to the first gun body, the partition is provided with a plurality of through holes, and the second gun body is provided with a molecular pump interface;

[0008] The inner surface of one end of the first gun body away from the second gun body is recessed outward to form a boss, and an insulator is placed on the boss, and the insulator includes a gate conductive ring, an aluminum cathode conductive ring, an inter-electrode insulating ceramic ring, a tungsten needle conductive column and a substrate, and the tungsten needle conductive column, the inter-electrode insulating ceramic ring, the aluminum cathode conductive ring and the gate conductive ring are coaxially distributed from the inside to the outside, and the tungsten needle conductive column, the inter-electrode insulating ceramic ring and the aluminum cathode conductive ring are welded together, and the inner surface of the gate conductive ring forms an integrated structure with the tungsten needle conductive column, the inter-electrode insulating ceramic ring and the aluminum cathode conductive ring through the substrate, and the substrate is placed on the boss of the first gun body; a ceramic air duct is provided inside the substrate, and the air outlet port of the ceramic air duct is located on the end surface of the substrate close to the second gun body, and the air inlet port of the ceramic air duct protrudes from the end surface of the substrate away from the second gun body; the gate conductive ring is connected to the first wire of the high-voltage cable, the tungsten needle conductive column is connected to the second wire of the high-voltage cable, and the aluminum cathode conductive ring is connected to the third wire of the high-voltage cable;

[0009] A tungsten needle is coaxially arranged at one end of the tungsten needle conductive column close to the second gun body;

[0010] An aluminum cathode is coaxially arranged on the outer surface of one end of the aluminum cathode conductive ring close to the second gun body. The surface of the end of the aluminum cathode away from the second gun body is flat, and the surface of the end of the aluminum cathode close to the second gun body is arranged to be a concave spherical surface. A ceramic sleeve is coaxially arranged on the outer surface of the aluminum cathode, and the gas outlet port of the ceramic gas guide tube is located between the grid and the ceramic sleeve.

[0011] A grid is coaxially arranged on the outer surface of the grid conductive ring, and the end surface of the grid close to the second gun body is arranged to be a smooth concave spherical surface. A ceramic washer is arranged on the end surface of the grid facing the insulator. The grid and the ceramic washer are provided with a central hole for a tungsten needle to pass through, and the end of the tungsten needle close to the second gun body does not exceed the end of the grid center hole close to the second gun body.

[0012] An anode coaxial with the tungsten needle is provided on the surface of one end of the partition facing the grid. The anode is a conical structure with a smooth outer surface protruding toward the grid. A center hole coaxial with the tungsten needle is provided in the center of the anode and the partition.

[0013] A beam guiding channel is provided at the end of the partition away from the grid, a center hole coaxial with the tungsten needle is provided at the center of the beam guiding channel, the end of the beam guiding channel away from the partition is sealedly connected to the end of the second gun body away from the partition, and an electromagnetic coil assembly is provided on the outer surface of the beam guiding channel.

[0014] Preferably, the tungsten needle conductive column and the aluminum cathode conductive ring are flush with the end surface close to the second gun body and protrude 8mm to 10mm from the end surface of the base close to the second gun body.

[0015] Preferably, the thickness between the inner surface and the outer surface of the inter-electrode insulating ceramic ring is 5mm to 10mm; the end surface of the inter-electrode insulating ceramic ring close to the second gun body is flush with the end surface of the tungsten needle conductive column and the aluminum cathode conductive ring close to the second gun body, or protrudes 3mm to 5mm from the end surface of the tungsten needle conductive column and the aluminum cathode conductive ring close to the second gun body.

[0016] Preferably, the end surfaces of the tungsten needle conductive column and the aluminum cathode conductive ring away from the second gun body both protrude more than 20 mm from the end surface of the substrate away from the second gun body 8, and the end surface of the inter-electrode insulating ceramic ring away from the second gun body is flush with the end surface of the substrate away from the second gun body 8.

[0017] Preferably, an electron gun top cover is sealed on one end of the first gun body away from the second gun body, the electron gun top cover is provided with through holes for the first wire of the high-voltage cable, the second wire of the high-voltage cable and the third wire of the high-voltage cable to pass through, and a through hole for the ceramic gas guide tube to pass through, and the gas inlet port of the ceramic gas guide tube protrudes from the surface of the end of the electron gun top cover away from the second gun body;

[0018] The insulator, the electron gun top cover and the first gun body form a closed cavity, and the cavity is filled with insulating oil.

[0019] Preferably, a metal sealing ring is installed on the outer edge of one end of the insulator away from the second gun body, and the metal sealing ring is threadedly connected to the inner surface of the first gun body.

[0020] Preferably, the electromagnetic coil assembly includes a scanning coil, a main focusing coil, a pre-focusing coil, an erasing coil, and an axis-coupling coil, which are sequentially arranged from one end of the beam guiding channel away from the partition and toward the partition, and the axis-coupling coil is fixed on the surface of the partition, the image-eliminating coil is fixed on the surface of the axis-coupling coil, and the pre-focusing coil is fixed on the surface of the image-eliminating coil.

[0021] A height-adjustable adjustment pad is provided between the main focusing coil and the scanning coil.

[0022] Preferably, the first gun body and the second gun body are connected by a hinge structure.

[0023] Preferably, the aluminum cathode conductive ring is connected to the aluminum cathode through threads, the aluminum cathode is connected to the ceramic sleeve through threads, and the gate conductive ring is connected to the gate through threads.

[0024] A method for using an indirect thermal electron gun, applicable to any of the indirect thermal electron guns described above, comprises the following steps:

[0025] S1. The external molecular pump connected to the molecular pump interface of the second gun body is started to make the vacuum degree inside the electron gun reach the set requirement. The external working gas is introduced into the discharge chamber composed of the grid, aluminum cathode and tungsten needle through the ceramic gas guide tube;

[0026] S2, the first conductor of the high-voltage cable will connect the negative high voltage -U HV -U p The second conductor of the high-voltage cable connects the negative high voltage -U HV The third conductor of the high-voltage cable will be the negative high voltage -U HV -U d The aluminum cathode is introduced through the aluminum cathode conductive ring, the -U p The voltage adjustment range is -10V to -2000V. dThe voltage adjustment range is -500V to -2000V. HV The voltage adjustment range is -60kV to -150kV;

[0027] S3, by adjusting -U d , the working gas between the aluminum cathode and the tungsten needle is discharged to generate plasma. The positive ions in the plasma bombard the aluminum cathode, and the secondary electrons generated by the aluminum cathode converge to the tungsten needle and heat the tungsten needle. When the temperature of the tungsten needle reaches the electron thermal generation state, an electron cloud is generated at the end of the tungsten needle.

[0028] S4, gradually reduce-U p , so that the electron cloud at the end of the tungsten needle emits electrons toward the anode. The electrons are gathered by the electrostatic field between the grid and the anode, forming an electron beam injection waist in the central hole of the anode;

[0029] S5. The electron beam gradually diverges after passing through the central hole of the anode, converges again after passing through the electromagnetic field generated by the pre-focusing coil, and then diverges again, and is focused again by the electromagnetic field of the main focusing coil to form an electron beam spot with highly concentrated energy on the surface of the workpiece for implementing the electron beam processing process.

[0030] Beneficial effects: Compared with the prior art, the present invention has the following significant beneficial effects:

[0031] 1. The present invention combines the advantages of existing hot cathode electron gun and cold cathode electron gun technologies, not only extending the cathode life, but also achieving a small electron beam spot with highly concentrated electron beam energy density, meeting the requirements of electron beam precision machining and manufacturing processes;

[0032] 2. The present invention can adjust the size of the electron beam current by adjusting the input gas flow rate and the grid voltage. Specifically: when the voltage applied to the aluminum cathode and the grid remains unchanged, the electron beam current is large when the input gas flow rate is large, and the electron beam current is small when the input gas flow rate is small; when the input gas flow rate and the acceleration voltage remain unchanged, the electron beam current is small when the grid voltage is large, and the electron beam current is large when the grid voltage is small;

[0033] 3. In the present invention, the gas in the electron gun is extracted through the molecular pump interface and several through holes of the partition, and the working gas is introduced into the discharge chamber through the ceramic gas guide tube, so that the vacuum degree at the tungsten needle and the aluminum cathode is low, which is conducive to the realization of low vacuum electron beam processing technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 Schematic diagram of the structure of the thermal electron gun of the present invention;

[0035] Figure 2 Schematic diagram of the structure of the insulator in the thermal electron gun of the present invention;

[0036] Figure 3 Schematic diagram of the electron beam trajectory of the thermal electron gun of the present invention;

[0037] Among them: 1. Insulator; 101. Ceramic gas guide tube; 102. Grid conductive ring; 103. Aluminum cathode conductive ring; 104. Inter-electrode insulating ceramic ring; 105. Tungsten needle conductive column; 2. Ceramic sleeve; 3. Aluminum cathode; 4. Grid; 5. Anode; 6. Ceramic gasket; 7. First gun body; 71. First sealing ring; 72. Second sealing ring; 8. Second gun body; 81. Molecular pump interface; 82. Third sealing ring; 83. Fourth sealing ring; 84. Spacer; 9. Beam guide Guide channel; 10. Tungsten needle; 11. Metal sealing ring; 12. Top cover of electron gun; 13. High-voltage cable; 131. First conductor of high-voltage cable; 132. Second conductor of high-voltage cable; 133. Third conductor of high-voltage cable; 14. Insulating oil; 15. Coil; 16. Erasing coil; 17. Pre-focusing coil; 18. Main focusing coil; 19. Adjustment pad; 20. Scanning coil; 21. Electron beam; 22. Electron beam injection; 23. Electron beam spot; 24. Workpiece. DETAILED DESCRIPTION

[0038] The present invention will be further described below with reference to the accompanying drawings.

[0039] In view of the current situation that the cathode life of hot cathode electron guns is short and it is difficult to adapt to situations such as large-scale metal structure additive manufacturing that require long-term stable operation of the electron gun, and the beam spot size of the electron beam output by cold cathode electron guns is large and it is difficult to adapt to high-precision electron beam processing and manufacturing needs such as large-scale metal structure additive manufacturing, the present invention discloses an indirect thermal electron gun, which combines the advantages of existing hot cathode electron gun and cold cathode electron gun technology, applies the electron generation technology of cold cathode gas discharge to the hot cathode electron gun, and replaces the electron emission technology of the two-pole electron gun composed of the filament and cathode in the existing hot cathode electron gun. It will effectively increase the service life of the cathode and meet the needs of electron beam precision processing and manufacturing technology.

[0040] The indirectly heated electron gun described in the present invention uses a cold cathode electron beam to heat a tungsten needle, causing the temperature of the tungsten needle to reach a thermal emission state to emit electrons, and controls the size of the electron beam emitted by the tungsten needle by a negative gate voltage. Then, through an electrostatic convergence system composed of the gate and the anode and an electromagnetic convergence system on the beam channel, the electron beam emitted by the tungsten needle obtains a small beam spot with highly concentrated electron beam energy on the surface of the workpiece, which is used for electron beam processing and is particularly suitable for the field of electron beam processing technology that requires high power, long cathode life, and highly concentrated beam spot energy.

[0041] The thermal electron gun of the present invention includes a first gun body 7 and a second gun body 8. The first gun body 7 and the second gun body 8 are both cylindrical structures. The facing end faces of the first gun body 7 and the second gun body 8 are connected. The second gun body 8 is provided with a third sealing ring 82. The second gun body 8 is sealed with the first gun body 7 through the third sealing ring 82. A partition 84 is provided at one end of the second gun body 8 close to the first gun body 7. The second gun body 8 is provided with a molecular pump interface 81 for connecting an external molecular pump.

[0042] The first gun body 7 and the second gun body 8 of the electron gun are connected by a hinge structure, which facilitates replacement of structural components such as the aluminum cathode 3 and the tungsten needle 10 in the first gun body 7 .

[0043] The inner surface of the end of the first gun body 7 away from the second gun body 8 is recessed outward to form a boss, on which the insulator 1 is placed. A second sealing ring 72 is provided on the boss, and the boss is sealed to the insulator 1 via the second sealing ring 72. A metal sealing ring 11 is mounted on the outer edge of the end of the insulator 1 away from the second gun body 8. The outer surface of the metal sealing ring 11 has external threads, and the inner surface of the first gun body 7, which is recessed outward, has internal threads. The external threads of the metal sealing ring 11 cooperate with the internal threads on the inner surface of the first gun body 7 to secure the insulator 1.

[0044] The insulator 1 includes a gate conductive ring 102, an aluminum cathode conductive ring 103, an inter-electrode insulating ceramic ring 104, a tungsten needle conductive column 105, and a substrate. The tungsten needle conductive column 105, the inter-electrode insulating ceramic ring 104, the aluminum cathode conductive ring 103, and the gate conductive ring 102 are coaxially arranged from the inside to the outside. The tungsten needle conductive column 105, the inter-electrode insulating ceramic ring 104, and the aluminum cathode conductive ring 103 are first welded together. The inner surface of the gate conductive ring 102 is integrated with the tungsten needle conductive column 105, the inter-electrode insulating ceramic ring 104, and the aluminum cathode conductive ring 103 through the substrate. The substrate is formed by an epoxy resin casting and curing process and is placed on the boss of the first gun body 7. A ceramic gas guide tube 101 is provided inside the substrate. The gas outlet of the ceramic gas guide tube 101 is located on the end surface of the substrate near the second gun body 8, and the gas inlet of the ceramic gas guide tube 101 protrudes from the end surface of the substrate away from the second gun body 8. The gate conductive ring 102 is connected to the first high-voltage cable conductor 131 of the high-voltage cable 13, wherein the gate conductive ring 102 is connected to the first high-voltage cable conductor 131 through a pre-buried conductor in the matrix, the tungsten needle conductive column 105 is connected to the second high-voltage cable conductor 132 of the high-voltage cable 13, and the aluminum cathode conductive ring 103 is connected to the third high-voltage cable conductor 133 of the high-voltage cable 13.

[0045] The ends of the tungsten needle conductive post 105 and the aluminum cathode conductive ring 103 that are adjacent to the second gun body 8 are flush with each other and protrude 8mm to 10mm from the base. An inter-electrode insulating ceramic ring 104 is disposed between the tungsten needle conductive post 105 and the aluminum cathode conductive ring 103 to insulate the tungsten needle conductive post 105 from the aluminum cathode conductive ring 103. The thickness of the inter-electrode insulating ceramic ring 104 between the inner and outer surfaces is 5mm to 10mm. The end of the inter-electrode insulating ceramic ring 104 that is adjacent to the second gun body 8 can be flush with the ends of the tungsten needle conductive post 105 and the aluminum cathode conductive ring 103 that are adjacent to the second gun body 8, or it can protrude 3mm to 5mm from the ends of the tungsten needle conductive post 105 and the aluminum cathode conductive ring 103 that are adjacent to the second gun body 8, further improving the insulation performance between the tungsten needle conductive post 105 and the aluminum cathode conductive ring 103. To facilitate heat dissipation, the end surfaces of the tungsten needle conductive column 105 and the aluminum cathode conductive ring 103 away from the second gun body 8 both protrude by more than 20 mm from the end surface of the substrate away from the second gun body 8, and the end surface of the inter-electrode insulating ceramic ring 104 away from the second gun body 8 is flush with the end surface of the substrate away from the second gun body 8.

[0046] An electron gun cover 12 is also provided at the end of the first gun body 7 facing away from the second gun body 8. The cover 12 is hermetically connected to the first gun body 7 via screws. A first sealing ring 71 is provided on the first gun body 7, sealing the connection between the first gun body 7 and the cover 12. The cover 12 is provided with a through hole for the high-voltage cable 13 and a through hole for the ceramic gas tube 101. The inlet port of the ceramic gas tube 101 protrudes from the surface of the cover 12 at the end facing away from the second gun body 8. The insulator 1, the cover 12, and the first gun body 7 form a sealed cavity filled with insulating oil 14. This filling not only improves the withstand voltage rating between the high-voltage cable 13 and the tungsten needle 10 and aluminum cathode conductive ring 103, but also serves to cool the electrodes.

[0047] The tungsten needle conductive column 105 is provided with a mounting hole for the tungsten needle 10 at one end close to the second gun body 8 . A locking structure is provided in the mounting hole for fixing the tungsten needle 10 . The tungsten needle 10 is coaxially arranged with the tungsten needle conductive column 105 .

[0048] The outer surface of the aluminum cathode conductive ring 103, located near the second gun body 8, is provided with an external thread for connecting to the aluminum cathode 3. The aluminum cathode 3 is coaxially arranged with the aluminum cathode conductive ring 103. The inner surface of the aluminum cathode 3 is provided with an internal thread, which cooperates with the external thread of the aluminum cathode conductive ring 103 to secure the aluminum cathode 3. The end surface of the aluminum cathode 3 away from the second gun body 8 is flat, while the end surface near the second gun body 8 is configured as an inwardly concave spherical surface. The outer surface of the aluminum cathode 3 is provided with an external thread for connecting to the ceramic sleeve 2. The ceramic sleeve 2 is coaxially arranged with the aluminum cathode 3. The inner surface of the ceramic sleeve 2 is provided with an internal thread, which cooperates with the external thread of the aluminum cathode 3 to secure the ceramic sleeve 2. The end surface of the ceramic sleeve 2 near the second gun body 8 is flush with the end surface of the aluminum cathode 3 near the second gun body 8 or protrudes from the end surface of the aluminum cathode 3 near the second gun body 8, thereby preventing gas discharge between the aluminum cathode 3 and the gate 4. The gas outlet port of the ceramic gas guide tube 101 is located between the grid 4 and the ceramic sleeve 2 .

[0049] The aluminum cathode 3 and tungsten needle 10 are equivalent to the cathode and anode of a cold cathode gas discharge electron gun. The positive ions in the plasma generated by gas discharge bombard the aluminum cathode 3, generating secondary electrons. The secondary electrons are accelerated by the electrostatic field formed by the aluminum cathode 3 and the tungsten needle 10 and bombard the tungsten needle 10, converting kinetic energy into thermal energy, heating the tungsten needle 10, and causing the tungsten needle 10 to reach a thermal emission state. Furthermore, in the present invention, the aluminum cathode 3 has a certain volume and heat capacity, is not easily deformed, and has a long lifespan. At the same time, the emitting end of the tungsten needle 10 (i.e., the end of the tungsten needle 10 away from the aluminum cathode 3) can be designed to be cylindrical, conical, or the like, to meet the requirements of different processes for electron beam spot quality. Furthermore, compared to "V"-shaped or mosquito coil-shaped filaments, the tungsten needle 10 is not easily deformed after being heated and can withstand particle erosion for a long time, thereby ensuring long-term electron beam spot quality and stable, high-quality output of the electron beam.

[0050] The outer surface of the gate conductive ring 102 is provided with an external thread for connecting the gate 4, and the gate 4 is coaxially arranged with the gate conductive ring 102; the inner surface of the end of the gate 4 away from the second gun body 8 is provided with an internal thread, and the internal thread of the gate 4 cooperates with the external thread of the gate conductive ring 102 to fix the gate 4. The surface of the end of the gate 4 close to the second gun body 8 is set to a smooth concave spherical surface. The gate 4 is connected to the negative high voltage-U through the gate conductive ring 102 and the first conductor 131 of the high voltage cable. HV -U p A ceramic washer 6 is provided on the end surface of the gate 4 facing the insulator 1 to prevent gas discharge between the gate 4 and the tungsten needle 10. The gate 4 and the ceramic washer 6 are provided with a central hole for the tungsten needle 10 to pass through. The end of the tungsten needle 10 close to the second gun body 8 generally does not extend beyond the end of the central hole of the gate 4 close to the second gun body 8.

[0051] The gate 4 applies a negative voltage lower than that of the tungsten needle 10. By adjusting the magnitude of the negative voltage of the gate 4, the electron beam current emitted by the tungsten needle 10 can be adjusted, that is, the magnitude of the electron beam current can be adjusted.

[0052] An anode 5 is disposed on the end surface of the separator 84 facing the grid 4. The anode 5 is a conical structure with a smooth outer surface that protrudes toward the grid 4. Both the anode 5 and the separator 84 have central holes for electron beam output. The central hole of the anode 5 is smaller than that of the separator 84. The anode 5, the central hole of the anode 5, and the central hole of the separator 84 are all coaxially arranged with the tungsten needle 10. Several through-holes are also uniformly arranged along the edge of the separator 84 to allow gas to circulate within the first and second gun bodies 7, 8. An external molecular pump maintains the required vacuum level for the first gun body 7 through the molecular pump interface 81 and these through-holes.

[0053] The anode 5 is grounded, and a high-voltage electric field is formed between the anode 5 and the gate 4 to accelerate the electrons emitted by the tungsten needle 10 . There is also an electrostatic field between the anode 5 and the gate 4 to generate an electrostatic convergence effect on the electrons emitted by the tungsten needle 10 .

[0054] A beam guiding channel 9 is provided at the end of the partition 84 away from the grid 4. A central hole is provided in the center of the beam guiding channel 9 for outputting the electron beam. The central hole of the beam guiding channel 9 has a larger diameter than that of the partition 84 and is coaxially arranged with the tungsten needle 10. The end of the beam guiding channel 9 away from the partition 84 is connected to the end of the second gun body 8 away from the partition 84. The end of the second gun body 8 away from the partition 84 is provided with an outer flange and a fourth sealing ring 83. The second gun body 8 is sealed to the beam guiding channel 9 via the outer flange and the fourth sealing ring 83. An electromagnetic coil assembly is provided on the outer surface of the beam guiding channel 9. The electromagnetic coil assembly includes a scanning coil 20, a main focusing coil 18, a pre-focusing coil 17, an erasing coil 16, and an axis-coupling coil 15, which are arranged in sequence from the end of the beam guiding channel 9 away from the partition 84 and toward the partition 84. The axis-coupling coil 15 is fixed to the surface of the partition 84, the image-coupling coil 16 is fixed to the surface of the axis-coupling coil 15, and the pre-focusing coil 17 is fixed to the surface of the image-coupling coil 16. That is, the positions of the axis-coupling coil 15, the image-coupling coil 16, and the pre-focusing coil 17 are fixed.

[0055] The coaxial coil 15 and the image-eliminating coil 16 are used to reduce beam spot distortion and optimize the quality of the electron beam.

[0056] The currents passing through the pre-focusing coil 17 and the main focusing coil 18 can be adjusted to adjust the working distance of the electron gun, that is, to adjust the position along the electron beam axis where the electron beam energy density reaches its maximum. Specifically, when the acceleration voltage and the height between the pre-focusing coil 17 and the main focusing coil 18 remain unchanged, the greater the current passing through the pre-focusing coil 17 and the main focusing coil 18, the stronger the magnetic field generated, the more significantly the electrons are affected by the magnetic field, the focus moves upward, and the effective working distance decreases.

[0057] An adjustable spacer 19 is provided between the main focusing coil 18 and the scanning coil 20 to adjust the distance between the pre-focusing coil 17 and the main focusing coil 18. That is, the object distance of the electromagnetic lens generated by the main focusing coil 18 can be adjusted to change the size of the beam spot on the workpiece surface, thereby adjusting the electron beam energy density on the workpiece surface and optimizing the electron beam quality.

[0058] The scanning coil 20 can generate two symmetrical radial alternating magnetic fields in the X direction and the Y direction to meet the requirements of special electron beam processing technology.

[0059] The working process of the thermal electron gun of the present invention is as follows:

[0060] (1) The external molecular pump connected to the molecular pump interface 81 of the second gun body 8 is started to make the vacuum degree inside the electron gun reach the set requirement, and the external working gas is introduced into the discharge chamber composed of the grid 4, the aluminum cathode 3, and the tungsten needle 10 through the ceramic gas guide tube 101;

[0061] (2) The first conductor 131 of the high-voltage cable connects the negative high voltage -U HV -U p Introduced into the gate conductive ring 102, so the gate 4 obtains a negative high voltage -U HV -U p , the second conductor 132 of the high-voltage cable will be negative high voltage -U HV The tungsten needle conductive column 105 is introduced, so the tungsten needle 10 obtains a negative high voltage -U HV , the third conductor 133 of the high-voltage cable will be negative high voltage -U HV -U d The aluminum cathode conductive ring 103 is introduced, so that the aluminum cathode 3 obtains a negative high voltage -U HV -U d ; said-U p The voltage adjustment range is -10V to -2000V. d The voltage adjustment range is -500V to -2000V. HV The voltage adjustment range is -60kV to -150kV;

[0062] (3) By adjusting -U d, the working gas between the aluminum cathode 3 and the tungsten needle 10 discharges to generate plasma. The positive ions in the plasma bombard the aluminum cathode 3. The secondary electrons generated by the aluminum cathode 3 converge toward the tungsten needle 10 and heat the tungsten needle 10. When the temperature of the tungsten needle 10 reaches the electron thermal generation state, an electron cloud is generated at the end of the tungsten needle 10;

[0063] (4) When the voltage on the gate 4 is high, the tungsten needle 10 cannot emit electrons to the anode 5, and the voltage on the gate 4 is gradually reduced. p , so that the electron cloud at the end of the tungsten needle 10 emits a certain number of electrons toward the anode 5, and the certain number of electrons are gathered by the electrostatic field between the grid 4 and the anode 5 to form an electron beam injection waist 22 in the central hole of the anode 5;

[0064] (5) The electron beam injection waist 22 gradually diverges after passing through the central hole of the anode 5, converges again after passing through the electromagnetic field generated by the pre-focusing coil 17, and then diverges again, and is focused again by the electromagnetic field of the main focusing coil 18, forming an electron beam spot 23 with highly concentrated energy on the surface of the workpiece 24 for implementing the electron beam processing process.

[0065] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. An indirect thermal electron gun, characterized in that: The invention comprises a first gun body (7) and a second gun body (8), wherein the first gun body (7) and the second gun body (8) are both cylindrical structures and their end faces are connected, a partition (84) is provided at one end of the second gun body (8) close to the first gun body (7), and the partition (84) is provided with a plurality of through holes, and the second gun body (8) is provided with a molecular pump interface (81); The inner surface of one end of the first gun body (7) away from the second gun body (8) is concave outward to form a boss, and an insulator (1) is placed on the boss, and the insulator (1) comprises a gate conductive ring (102), an aluminum cathode conductive ring (103), an inter-electrode insulating ceramic ring (104), a tungsten needle conductive column (105) and a substrate, and the tungsten needle conductive column (105), the inter-electrode insulating ceramic ring (104), the aluminum cathode conductive ring (103) and the gate conductive ring (102) are coaxially distributed from the inside to the outside, and the tungsten needle conductive column (105), the inter-electrode insulating ceramic ring (104) and the aluminum cathode conductive ring (103) are welded together, and the inner surface of the gate conductive ring (102) is connected to the tungsten needle conductive column (105) through the substrate. 105), an inter-electrode insulating ceramic ring (104), and an aluminum cathode conductive ring (103) form an integrated structure, and the substrate is placed on a boss of the first gun body (7); a ceramic air duct (101) is provided inside the substrate, an air outlet port of the ceramic air duct (101) is located on an end surface of the substrate close to the second gun body (8), and an air inlet port of the ceramic air duct (101) protrudes from an end surface of the substrate away from the second gun body (8); the gate conductive ring (102) is connected to a first conductor (131) of a high-voltage cable, the tungsten needle conductive column (105) is connected to a second conductor (132) of the high-voltage cable, and the aluminum cathode conductive ring (103) is connected to a third conductor (133) of the high-voltage cable; A tungsten needle (10) is coaxially arranged at one end of the tungsten needle conductive column (105) close to the second gun body (8); An aluminum cathode (3) is coaxially arranged on the outer surface of one end of the aluminum cathode conductive ring (103) close to the second gun body (8); the surface of the end of the aluminum cathode (3) away from the second gun body (8) is flat, and the surface of the end of the aluminum cathode (3) close to the second gun body (8) is arranged to be a concave spherical surface; a ceramic sleeve (2) is coaxially arranged on the outer surface of the aluminum cathode (3); and the gas outlet port of the ceramic gas guide tube (101) is located between the grid (4) and the ceramic sleeve (2); A gate (4) is coaxially arranged on the outer surface of the gate conductive ring (102), and the surface of the gate (4) at one end close to the second gun body (8) is arranged to be a smooth concave spherical surface. A ceramic washer (6) is arranged on the surface of the gate (4) at one end facing the insulator (1). A central hole for a tungsten needle (10) to pass through is arranged on the gate (4) and the ceramic washer (6), and the end of the tungsten needle (10) close to the second gun body (8) does not exceed the end of the central hole of the gate (4) close to the second gun body (8); An anode (5) coaxial with the tungsten needle (10) is provided on the surface of one end of the partition (84) facing the grid (4); the anode (5) is a conical structure with a smooth outer surface protruding toward the direction where the grid (4) is located; and a center hole coaxial with the tungsten needle (10) is provided in the center of both the anode (5) and the partition (84); A beam guiding channel (9) is provided at one end of the partition (84) away from the grid (4), a center hole coaxial with the tungsten needle (10) is provided at the center of the beam guiding channel (9), the end of the beam guiding channel (9) away from the partition (84) is sealedly connected to the end of the second gun body (8) away from the partition (84), and an electromagnetic coil assembly is provided on the outer surface of the beam guiding channel (9).

2. The indirect thermal electron gun according to claim 1, characterized in that: The tungsten needle conductive column (105) and the aluminum cathode conductive ring (103) are flush with one end surface close to the second gun body (8) and protrude 8mm to 10mm from the one end surface of the base close to the second gun body (8).

3. The indirect thermal electron gun according to claim 1, characterized in that: The thickness between the inner surface and the outer surface of the inter-electrode insulating ceramic ring (104) is 5mm to 10mm; the end surface of the inter-electrode insulating ceramic ring (104) close to the second gun body (8) is flush with the end surface of the tungsten needle conductive column (105) and the aluminum cathode conductive ring (103) close to the second gun body (8), or protrudes 3mm to 5mm from the end surface of the tungsten needle conductive column (105) and the aluminum cathode conductive ring (103) close to the second gun body (8).

4. The indirect thermal electron gun according to claim 1, characterized in that: The end surfaces of the tungsten needle conductive column (105) and the aluminum cathode conductive ring (103) away from the second gun body (8) both protrude more than 20 mm from the end surface of the substrate away from the second gun body 8, and the end surface of the inter-electrode insulating ceramic ring (104) away from the second gun body (8) is flush with the end surface of the substrate away from the second gun body 8.

5. The indirect thermal electron gun according to claim 1, characterized in that: An electron gun top cover (12) is sealed on one end of the first gun body (7) away from the second gun body (8); the electron gun top cover (12) is provided with through holes for a first high-voltage cable conductor (131), a second high-voltage cable conductor (132), and a third high-voltage cable conductor (133) to pass through, as well as a through hole for a ceramic air guide tube (101) to pass through; an air inlet port of the ceramic air guide tube (101) protrudes from a surface of one end of the electron gun top cover (12) away from the second gun body (8); The insulator (1), the electron gun top cover (12) and the first gun body (7) form a closed cavity, and the cavity is filled with insulating oil (14).

6. The indirect thermal electron gun according to claim 5, characterized in that: A metal sealing ring (11) is installed on the outer edge of one end of the insulator (1) away from the second gun body (8), and the metal sealing ring (11) is threadedly connected to the inner surface of the first gun body (7).

7. The indirect thermal electron gun according to claim 1, characterized in that: The electromagnetic coil assembly comprises a scanning coil (20), a main focusing coil (18), a pre-focusing coil (17), an image-eliminating coil (16) and an axis-coupling coil (15) which are sequentially arranged from one end of the beam guiding channel (9) away from the partition (84) and toward the partition (84), wherein the axis-coupling coil (15) is fixed on the surface of the partition (84), the image-eliminating coil (16) is fixed on the surface of the axis-coupling coil (15), and the pre-focusing coil (17) is fixed on the surface of the image-eliminating coil (16); A height-adjustable adjustment pad (19) is provided between the main focusing coil (18) and the scanning coil (20).

8. The indirect thermal electron gun according to claim 1, characterized in that: The first gun body (7) and the second gun body (8) are connected via a hinge structure.

9. The indirectly heated electron gun according to claim 1, characterized in that: The aluminum cathode conductive ring (103) is connected to the aluminum cathode (3) through a threaded connection, the aluminum cathode (3) is connected to the ceramic sleeve (2) through a threaded connection, and the gate conductive ring (102) is connected to the gate (4) through a threaded connection.

10. A method for using an indirect thermal electron gun, applied to the indirect thermal electron gun according to any one of claims 1 to 9, characterized in that: The steps include: S1, the external molecular pump connected to the molecular pump interface (81) of the second gun body (8) is started to make the vacuum degree inside the electron gun reach the set requirement, and the external working gas is introduced into the discharge chamber composed of the grid (4), the aluminum cathode (3), and the tungsten needle (10) through the ceramic gas guide tube (101); S2, the first conductor of the high-voltage cable (131) connects the negative high-voltage HV -U p The negative high voltage -U is introduced into the gate (4) through the gate conductive ring (102), and the second conductor (132) of the high voltage cable HV The tungsten needle (10) is introduced through the tungsten needle conductive column (105), and the third conductor (133) of the high-voltage cable transmits the negative high voltage -U HV -U d The aluminum cathode (3) is introduced through the aluminum cathode conductive ring (103), and the p The voltage adjustment range is -10V to -2000V. d The voltage adjustment range is -500V to -2000V. HV The voltage adjustment range is -60kV to -150kV; S3, by adjusting -U d , causing the working gas between the aluminum cathode (3) and the tungsten needle (10) to discharge and generate plasma, the positive ions in the plasma bombard the aluminum cathode (3), the secondary electrons generated by the aluminum cathode (3) converge toward the tungsten needle (10) and heat the tungsten needle (10), and when the temperature of the tungsten needle (10) reaches an electron heat generation state, an electron cloud is generated at the end of the tungsten needle (10); S4, gradually reduce-U p , causing the electron cloud at the end of the tungsten needle (10) to emit electrons toward the anode (5), and the electrons are gathered through the electrostatic field between the grid (4) and the anode (5), forming an electron beam injection waist (22) in the central hole of the anode (5); S5. The electron beam injection waist (22) gradually diverges after passing through the central hole of the anode (5), converges again after passing through the electromagnetic field generated by the pre-focusing coil (17), and then diverges again, and is focused again by the electromagnetic field of the main focusing coil (18), forming an electron beam spot (23) with highly concentrated energy on the surface of the workpiece (24) for implementing the electron beam processing process.

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